The support module's APD bias has come factory set for an APD
multiplication gain between 10 and 20. The APD bias monitor via the BNC
connector is provided as a way to check the bias and adjust it as
desired. You do not need to have the APD bias monitored while the
module is in operation, but it is good idea to double check its value at
least intermittently. A simple voltmeter can be used to check the bias,
and any BNC type connection and cabling should work fine. The
specifications sheet has a chart showing the APD's DC current and gain
versus it bias, as well as a table listing the bias at M=10 and M=20.
While a current-limiter in the support module protects from damaging the
APD, you must keep the APD bias below breakdown to prevent a noisy output.
The SMA outputs are designed for 50-Ohm coax cabling. Since
your receiver has 300 MHz output filters most cabling should work fine.
Higher frequency RF or microwave rated cabling is not required. Closely
matching cable length for the two outputs is required when you are
terminating the two outputs differentially, otherwise when using single
ended outputs ensure that both outputs are terminated similarly.
In terms of the support module's ground, it should be provided
through the power supply's IEC connector to a safety earth. For signal
integrity the receiver's outputs should be grounded through the SMA coax
cabling to whatever instrument you are using read the output, i.e.
oscilloscope or counter. The ground plug is an optional ground
connected directly to the outputs' SMA coax ground, but it is not
required for operation.
I am also attaching an electronic copy of the specifications and
operations sheets if more copies of it are needed.